The present invention relates to a novel construction technique, and apparatus for performing said technique, for deposition of cementitious material, optionally with the controlled application of "accelerators". The present invention also relates to an apparatus and technique for deposition of multiple layers of cementitious material, said cementitious material preferably being further dosed with one or more accelerator compounds at the point at which it is deposited, thereby allowing application of further layers onto the partly cured cementitious material without said material deforming unduly under the weight of the additional layer(s).

Rapid prototyping has grown in use enormously over the last decade in various fields of industrial design moving from being a niche technique into the mainstream with various techniques offering a choice of materials, resolution and assorted other factors. Amongst the more common techniques are stereolithography, selective laser sintering (SLS) and fused deposition modelling (FDM), with the latter two both being additive manufacturing techniques mostly used with plastics materials, with FDM in particular also being used for rapid manufacture of short run, or small batch size, plastics components. The present invention seeks to take the advantages offered by rapid prototyping techniques to the fields of product design and manufacture and introduce them to the field of construction, in effect providing a 3D printer capable of "printing" large complex, irregular objects and structures formed from cementitious materials. Several attempts have been made to deliver some of the advantages offered by the present invention, however, all have their shortcomings and are generally extremely limited in terms of either or both of the size of object / structure which can be produced and also the complexity of said object / structure. The term "accelerating agent" should be taken to include any material that is capable of accelerating, via catalytic or other processes, the curing / setting of cementitious material.

The term "retarder" should be taken to refer to any material which retards or slows the curing / setting of cementitious material. This may lengthen the open time for workability and / or improve the Theological properties for workability, extrudability, printability and buildability.

The term "cementitious material" or "cemented material" should be taken to include any agglomeration of filler(s) and binder(s) that can be conveyed in a fluid state and then harden after deposition.

The term "stabilised cementitious material" refers to a cementitious material which has a retarder added thereto.

The term "support material" refers to a material which is temporarily deposited to act as a support for subsequent layers of construction, said support material being removed and optionally recovered / recycled for subsequent reuse upon completion of said construction.

The terms "cartilage material" and "cartilage layer" refer to a material or layer imposed in between the support and cementitious layers, or over the finished surfaces, or around any internal or external feature that improves the ease of separation of these layers, separates the surface of the built component from another fluid e.g. to minimise evaporation of water or loss of other compound from the cementitious material during curing, to improve the surface finish of the cementitious material and / or to enable the creation of a textured finish to said cementitious material. This layer may be temporary, semi-permanent or may form a permanent feature of the completed component. The term "work surface" refers not only to the virgin surface upon which construction is commenced, but also to the uppermost exposed layer of any or all of the cementitious material, the support material and the cartilage material.

The term "substantially simultaneously" specifically with reference to the description of the interrelation of the deposition of the cementitious and support materials should be construed broadly, in as much as it is unlikely to be the case that any given layer will require identical amounts and even distributions of both cementitious and support materials, therefore there will inevitably be instances where support material is being deposited whilst cementitious material is not and vice versa, hence this terminology should be taken to infer that said deposition of the cementitious and support materials may be synchronous, although precise synchronicity is not required.

The term "activation agent" should be taken to include any material that is capable of accelerating, via catalytic or other processes, the curing / setting of the support material.

Where the term "nozzle" is used, it should be taken to indicate either a single nozzle or a plurality of nozzles located proximal one another, hence the singular should be construed as to also include the plural and vice versa.

The present invention overcomes the shortcomings of the prior art / state of the art and provides, in a first aspect, a multi-layer construction method with construction of each layer comprising the steps of:

providing a cementitious material;

delivering said cementitious material to a nozzle;

indexing said nozzle along a pre-determined path; and

applying said cementitious material to a work surface by extrusion through said nozzle; and

these steps being repeated for each additional layer of construction required.

Preferably the cementitious material is a stabilised cementitious material. Preferably the cementitious material is stabilised prior to delivery of the cementitious material to the nozzle and prior to applying the cementitious material to the work surface. Preferably said cementitious material is a concrete material.

Preferably said method features the additional step of applying an accelerating agent to said cementitious material, said application of said accelerating agent may be before, during or after said extrusion of said cementitious material. Said stabilised cementitious material may be agitated, through vibration, stirring, mixing or any other commonly known method, thereby reducing friction between said cementitious material and the internal surfaces of an apparatus being used to deliver it. Said indexing of said nozzle along said predetermined path is preferably computer controlled.

The method preferably further comprises, substantially simultaneously with said application of said cementitious material, applying a support material in a contiguous layer with said cementitious material in areas where cementitious material is not desired, such that said support material, along with said cementitious material, provides the work surface for the next layer of construction. Preferably said method further comprises exposing said support layer to an activation agent.

Said method may further comprise the application of a cartilage layer to the upper surface of the support layer in areas where the subsequent layer is to be one of cementitious material. The addition of said cartilage layer serves to improve the surface finish of the cementitious material whilst simultaneously improving the structural integrity of the finished construction through minimising the amount of moisture lost from the cementitious material whilst it is curing. The method may further comprise the use of one or more cameras to capture real-time information relating to surface texture and / or deformation of the work surface, said information being used to determine application conditions necessary for the current layer being applied, said application conditions being selected from number of nozzles, nozzle size, nozzle orientation, flow rate of cementitious material, velocity of nozzle indexing and rate or timing of application of accelerating agent.

The application / delivery of any of the cementitious material, the support material, the cartilage layer or material, or the accelerator can be performed via a vibratable nozzle or by a variable diameter nozzle or both.

A second aspect of the present invention provides apparatus for performing a multi-layer construction method as described above, said apparatus comprising a reservoir of a cementitious material, said reservoir being functionally connected to a nozzle, means for indexing said nozzle along a pre-determined path, means for controlling the flow of said cementitious material from said reservoir to said nozzle and extruding said material out of said nozzle.

Preferably, the reservoir of cementitious material comprises a reservoir of stabilised cementitious material. The reservoir may be of any size that allows for buffering of discontinuous, but pressure-controlled, flow from the nozzle. Preferably, said apparatus further comprises means for applying an accelerating agent to said cementitious material.

Said apparatus may further comprise agitation means in functional communication with said reservoir and / or said functional connection between said reservoir and said nozzle.

The apparatus preferably further comprises computer control means, said control means controlling the indexing of said nozzle, the flow rate of said cementitious material and the timing and rate of application of said accelerating agent.

Said indexing means preferably comprise a robotic arm, said robotic arm preferably being capable of both indexing along three independent axes and also capable of multi axis rotation of said nozzle.

The apparatus preferably further comprises a reservoir of support material, said reservoir being functionally connected to a support material application nozzle, means for indexing said nozzle along a pre-determined path, means for controlling the flow of said support material from said reservoir to said nozzle and extruding said material out of said nozzle.

Said apparatus preferably also comprises means for applying an activation agent to said support material. Said apparatus may further comprise a reservoir of cartilage material, said reservoir being functionally connected to a cartilage material application nozzle, means for indexing said nozzle along a pre-determined path, means for controlling the flow of said cartilage material from said reservoir to said nozzle and extruding said material out of said nozzle.

In a particularly preferred embodiment, said apparatus further comprises one or more cameras, said one or more cameras being either static, mounted to said robotic arm or independently indexable to track said extrusion nozzle, said cameras being capable of capturing information relating to texture, shape or form, said one or more cameras being capable of transferring said information to said computer control unit, said computer control unit being capable of interpreting said information and subsequently using said information to inform control of said one or more extrusion nozzles and the flow of said one or more materials from said one or more reservoirs to said one or more nozzles. Any one or more of the nozzles for applying / delivering / extruding cementitious material, support material, cartilage material or accelerator may be a vibratable nozzle or a variable diameter nozzle or both.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of a delivery apparatus for performing multi-layer delivery of a cementitious material;

Figure 2 is a schematic diagram of a print head incorporating two deposition heads, for use with the delivery apparatus of figure 1 ;

Figures 2a and 2b are schematic diagrams illustrating dispositions of the deposition heads of the print head of figure 2 during deposition;

Figure 3 is a schematic partial cross-sectional diagram of the cementitious material deposition head which forms part of the print head of figure 2 together with supporting delivery mechanism for delivery of cementitious material;

Figure 3a is a schematic side view of the print head;

Figure 4 is a schematic diagram of a delivery mechanism for accelerator and cartilage material, an optical measurement system and a robotic control mechanism suitable for use with the apparatus of figure 1 ;

Figure 5 is a schematic cross-sectional view of a sand and binder deposition head suitable for use with the apparatus of figure 1 ;

Figure 6 is a schematic diagram of a sand delivery mechanism suitable for use with the deposition head of figure 5;

Figure 7 is a schematic cross-sectional diagram of a cementitious material stirrer suitable for use with the apparatus of figure 1 ;

Figure 8 is a schematic diagram of a vibrating nozzle suitable for use with the print head of figure 2; and

Figure 9 is a schematic diagram of a variable nozzle suitable for use with the print head of figure 2. Figure 1 shows a delivery apparatus 100 for delivery of a cementitious material to a nozzle 13, the spatial position and orientation of which nozzle can be controlled robotically. The delivery apparatus 100 performs what may be described as a "printing" process using a delivery pump 2 to deliver the cementitious material to a nozzle 13. A worm pump 2 in combination with a hopper 102 is coupled to a deposition head 6 by way of a delivery pipe 3. The deposition head 6 is mounted on a robotic arm assembly 1 which is configured to provide automated freedom of movement to the deposition head 6. The robotic arm assembly 1 is controlled by a main controller 110. Preferably, the robotic arm assembly 1 enables the deposition head 6 to be moved, i.e. indexed along all three orthogonal axes together or independently and also allows the nozzle 13 to be rotated about all three orthogonal axes allowing a full six degrees of freedom. Thus, in a general aspect, the robotic arm assembly 1 provides a means for indexing the nozzle along a predetermined path. The deposition head 6 forms part of a multi-function print head 101 which is mounted on a distal arm 103 of the robotic arm assembly 1. The distal arm 103 also supports a piston 5 and a reservoir 4 for delivery of the cementitious material to the nozzle 13. In use, the worm pump 2 delivers cementitious material from the hopper 102 to the reservoir 4 through the delivery pipe 3.

The cementitious material may be continuously agitated to maintain a suitable rheological state. The reservoir 4 may eliminate unwanted high pressure built up by the worm pump 2 during delivery of the material to the deposition head 6 in order to have a precise control of extrusion of the cementitious material. The cementitious material is preferably delivered from the reservoir 4 by the piston 5 to the deposition head 6, and to the nozzle 3 with adjustable flow-rate, and extruded along a pre-defined path controlled by the main controller 110 driving the robotic arm assembly 1. A retarder is preferably added to the cementitious material before it is loaded into the hopper 102, or when it is already in the hopper 102, so as to provide a reservoir of stabilised cementitious material. Alternatively, a retarder could be added downstream as discussed later.

Figure 2 shows in greater detail the print head 101 and the multi-axis rotation of the nozzle 13 and the print head 101. The print head 101 consists of a motor 7, a gearbox 8, a one way bearing 9, the deposition head 6 for cementitious material (also described herein as the "first" deposition head)and its nozzle 13, and a second deposition head 11 for support material and its nozzle 12. The print head 101 is rotatable about an axis orthogonal to the plane of the drawing of figure 2 as shown in figures 2a and 2b. The rotational freedom of the robotic arm assembly 1 allows the first and second deposition heads 6, 11 to be positioned for deposition of material relative to a surface 104 or 105a or 105b and to remain orientated normal to the surface 104, 105a, 105b being built within the confines of each axis. This allows for the creation of concave or convex curved surfaces 105a, 105b while minimising the risk of collision between the nozzles 12, 13 and the printed surface (e.g. particularly concave surface 105a), as well as allowing a fixed vertical orientation for building horizontal layers 104.

Figure 3 shows further details of the print head 101 and the cementitious material delivery mechanism. Piston 5 has a piston cylinder 16 driven by air from an air inlet 17. The piston cylinder 16 is configured to drive a piston head 106 within the reservoir 4 via piston rod 107. Piston head 106 includes a sealing ring 20 and one or more magnets 19 which are configured to actuate magnetic switches 22A, 22B by proximity thereto, to indicate first and second positions of the piston head 106. A switch logic circuit 21 is configured to monitor the state of the magnetic switches 22A, 22B and to provide feedback to the main controller 110. The delivery pipe 3 is coupled to the end of the reservoir 4 for delivery of cementitious material. The cementitious material deposition head 6 on the print head 101 is coupled to the reservoir 4 by a transfer hose 18 which is clamped to the deposition head 6 by clamps 25, 27. A pump roller plate 23 carries a plurality of rollers 24 and is configured to rotate about an axis 108 such that each roller 24 can successively compress the transfer hose against a curved pressure shoe 28, similar to the design of a peristaltic pump.

In use, stabilised cementitious material is delivered by driving the piston cylinder 16 by injecting air through the air inlet 17, to drive piston head 106 towards switch 22B thereby expelling stabilised cementitious material from the reservoir 4, through the transfer hose 18, and to the deposition head 6. The cementitious material in the transfer hose 18 is extruded by the rollers 24 on the pump roller plate 23 rotating clockwise as viewed in figure 3, causing the cementitious material to be extruded through the nozzle 13. When the piston head magnets 19 trigger the lower switch 22B, the switch logic circuit 21 sends a signal to the main controller 110 to stop injecting air through the air inlet 17 and pump material through the delivery pipe 3. Cementitious material is thereby pumped into the reservoir 4 to refill the reservoir. This could be assisted by injecting air into a second air inlet 17A to drive piston cylinder 16 and piston head 106 upwards. The main controller 110 may also, during the refilling of reservoir 4, stop rotation of the pump roller plate 23 and movement of the robotic arm assembly to allow time for the refilling, before resuming operation after the reservoir refilling is complete. A retarder could be added to the cementitious material when charging the reservoir 4.

The piston arrangement preferably provides a constant pressure to the deposition head 6 and / or nozzle 13. This function could alternatively be performed by any suitable mechanism for controlling pressure and flow of material from a reservoir or supply to the deposition head and / or nozzle. For example, a bladder- or diaphragm-based system could be used.

The main controller 110 generally controls the flow rate of the cementitious material through the nozzle 13 in concert with the motion or indexing of the nozzle.

Figure 3 also shows in the inset diagram figure 3a, a front view of the print head 101 which is depicted in end cross-section in the main part of the figure. The cementitious material to be used in the delivery mechanism just described may be of any suitable type as discussed earlier, but should preferably be developed according to criteria such as: workability, pumpability, extrudability, printability and buildability, optimised for a three-dimensional concrete printing process. Figure 4 depicts a real-time feedback system using an optical measuring device 32, and also shows further features of the print head 101 for delivery of accelerator and / or cartilage material.

The feedback system comprises an optical sensor 32, a measurement processor 33 and an interface 34 with the main controller 110 of the robotic arm assembly 1. The optical sensor may comprise one or more cameras for viewing the layers of material being built up by extrusion from either one of the deposition heads 6 and 11. The optical sensor 32 (or plural sensors) may be static or mounted to a part of the robotic arm assembly 1 or may be mounted to the print head 101. Alternatively, the optical sensor or sensors 32 could be mounted to a separately moveable or indexable structure, e.g. on a separate track or a robotic arm. The optical sensor 32, e.g. camera, is preferably configured to capture information relating to texture, shape or form of the material deposited by either or both of the deposition heads 6, 11. In use, the feedback system may measure some or all of the continuity, width, height and reflectance of the extruded bead (e.g. of cementitious material or other material to be described later) during deposition as well as any vertical, horizontal or other deformation of previously built layers. The feedback system may also monitor information relating to the surface finish and texture and three-dimensional location of the extruded bead and / or previously built layers with reference to the instructions generated from the computer model. Such information is processed in real-time in the measurement processor 33, and any variations to the set parameters may instigate changes to the deposition process, pump speed, velocity of travel by controlling the robot interface 34 and system pause, etc. Variations to the set parameters may be made "on the fly" as the material is deposited such that there is real-time feedback to the delivery apparatus to control current parameters being used to deposit the current layer being deposited. Alternatively, variations to the set parameters may be made to control future parameters, e.g. for the next deposited layer so as to "correct" or "repair" deviations from the intended profile of a previous layer or layers. Variations to the set parameters may include any of the operational parameters of the deposition apparatus such as to the pumps or nozzles or robotic arm assembly to control flow rates, height or position of the material being deposited.

The print head 101 or delivery mechanism may further include a container 29 for an accelerator ("accelerating agent") and a container 30 for cartilage material. Each of these containers 29, 30 is coupled to a nozzle 35 by way of delivery pipes 111 , 1 12 and a solenoid valve 31 which is under the control of the measurement processor 33. The nozzle 35 may be integrated with the cementitious material nozzle 13 in the form of a multi-chamber nozzle. Alternatively, the nozzle 35 could be adjacent to, or concentric with, the cementitious material nozzle 13, e.g. forming a shroud.

The accelerating agent and / or cartilage material may therefore be delivered through a nozzle 35 that is one or more of coaxial with, adjacent to, or at least partially surrounding the cementitious material nozzle 13. The accelerating agent nozzle and / or cartilage material nozzle 35 may comprise a circumferential shroud around the cementitious material nozzle 13 or may be incorporated within the cementitious material nozzle 13. This enables the cartilage material to be conveniently built up in layers simultaneously with, or interspersed with, the cementitious material, or as a base layer, intermediate layer or cap layer to the or each cementitious layer. Exemplary cartilage materials can include latex, gelatin, vinyl, metals (e.g. for electrical conductivity, finish or structural enhancement), expanding foam (e.g. for thermal insulation), resins, powders, textiles, dyes, inks and other surface finishes, or property-enhancing materials.

In use, the solenoid valve 31 controls the delivery of accelerator and cartilage material from the containers 29, 30 to be deposited through the nozzle 35. The systems of figure 4 for delivery of accelerator and cartilage material are shown as gravity fed systems. However, it is possible also to replace either of these with a pumped system. For example, a peristaltic pump could meter delivery of either or both accelerator or cartilage material to the nozzle 13.

Thus, in a general aspect, the container 29, valve 31 , delivery pipe 111 and nozzle 35 or 13 provides an exemplary means for applying an accelerating agent to the stabilised cementitious material, and the main controller 110, interface 34 exemplify apparatus to control the flow rate of the timing and rate of application of an accelerating agent.

An accelerator for the build (cementitious) material may comprise sulphuric, aluminium salt and diethanolamine, and can be selected to control the setting time of the cementitious material. The accelerator may be mixed with a retarder, e.g. formed by amino-tris (methylenephosphonic acid), citric and formaldehyde, to secure a sufficient open time to ensure layer buildability. Preferably some retarder is premixed with the cementitious material provided in the hopper 102 and delivered to the deposition head 6. This provides a greater open time for use of the cementitious build material. Preferably, accelerator is added later than the retarder, e.g. at the nozzle 13 to shorten the stiffening time after deposition of the material.

Accelerator and cartilage materials in the containers 29, 30 of Figure 4 may be held under low pressure in the containers 29 and 30. When solenoid valve 31 is energized in such a manner as to allow passage of material from either container 29 or 30 into the nozzle 35, deposition onto the previously laid surface is coated with material from the selected container 29, 30. As mentioned earlier, the nozzle 35 may comprise a shroud which may consist of separated segments within, and may be rotatable to orientate in the direction of travel of the deposition head 6 along a work piece being constructed. Thus, in a general aspect, the print head 101 in combination with the containers 29, 30, solenoid valve 31 , delivery pipes 111, 112 and nozzle 13, 35 provide a reservoir for accelerating agent, a reservoir for cartilage material and means for delivering the accelerating agent and cartilage material to a nozzle for extrusion therefrom.

Figure 5 shows further detail of the deposition head 11 for support material. Exemplary support material could be binder and sand. The binder is stored in a binder container 36 coupled to a mixing chamber 115 by a binder pump 37 and a binder entry point 38 of the mixing chamber 115. The support material (e.g. casting sand) is deliverable through a sand entry point 39 from a suitable container, not shown. The mixing chamber 115 includes mixing paddles 41 , 42 for mixing the sand and binder. The paddles 41 , 42 are rotated by a suitable motor 46 and shaft 117, which also rotates an anti-lodging rod 66 within the nozzle 12. Plates 43A, 43B have apertures 43.

In use, the mixed sand and binder is passed through the apertures 43 in the plates 43A, 43B which are size adjustable to regulate the rate at which the mixed material falls through, to control the mixing time in the mixing chamber 115 in order to maintain the degree of mixing. The mixed material is then extruded through the nozzle 12. The amount of support material in the mixing chamber 115 is controlled by a metering unit 40 comprising a rotating cylinder 118 with slits 119, and flow-rate of the support material is measured and controlled by a variable reluctance pickup 47 and a pump speed control circuit 48. As the shaft 117, mixing paddles 41, 42 and anti-lodging rod 66 rotate, the variable reluctance pickup creates a variable frequency signal according to the speed of rotation. The measurement made by the variable reluctance pickup could alternatively be generated by other devices, such as Hall-effect or optical devices, for example. This variable frequency signal is fed to a frequency-to-voltage converter and then to a pulse width modulation (PWM) circuit to drive the binder pump 37. The binder pump is preferably driven so as to maintain a desired or constant sand binder ratio. The rotation of anti-lodging rod 66 prevents residues building up inside the nozzle 12.

In a general aspect, the mixing chamber 115 provides an exemplary reservoir for support material for delivery to the nozzle 12 and the main controller 110 further controls the rate of flow of the support material to the nozzle by way of the motor 46 and binder pump 37.

An accelerator or "activation agent" for the support material may be delivered by way of an accelerator delivery pipe 44 to the nozzle 12. As shown, the nozzle 12 may be a multi-port nozzle and may include a shroud nozzle arrangement 45 to deliver the activation agent for the support material. The activation agent may therefore be delivered through a nozzle 45 that is one or more of coaxial with, adjacent to, or at least partially surrounding the support material nozzle 12. In one arrangement as shown, the activation agent nozzle 45 may comprise a circumferential slot around the support material nozzle 12. Another arrangement might be that the activation agent is mixed into the support material within the support material nozzle 12.

Such arrangements as described above are ideally suited for dispensing casting sand or another suitable powdered material that is set with a gaseous material, such as C0 ₂ . Moist sand, e.g. generated by the deposition head 11 mixing sand from entry point 39 with a wet binder material (e.g. water) from binder container 36), is set with the C0 ₂ . This enables the support material to be conveniently built up in layers in a similar manner to that of the cementitious material. As discussed earlier, support materials may be used which can be removed and possibly recycled after deposition, e.g. after construction of an article, or after deposition of subsequent layers of cementitious material. For example, a sand-based support material can be flushed with water during a later stage of the process. An exemplary activation agent for the support material may be carbon dioxide (C0 ₂ ), applied under low pressure to the mixed support material which accelerates the reaction between silica sand and sodium silicate, by causing desiccation. The accelerator may be delivered from an external cylinder (not shown), equipped with 6 mm pipe 44, and passed through a solenoid valve (not shown) to the exit nozzle 12 via the shroud 45. Thus, the support material can be activated during deposition.

Figure 6 shows further details of a mechanism for delivery of the sand component of the support material. The support material, e.g. dry silica sand, is blown through a delivery tube 55 from a bulk container 49 using low pressure compressed air, which is added through the air gauge 58 and needle valve 50, into a small reservoir 56 mounted near to the extreme end of the robotic arm assembly 1. Exhaust air from the reservoir 56 is regulated by the needle valve 52 and air tube 54 to reduce the velocity of dry sand to the deposition head 11 for the support material. During the periods of inactivity of support material deposition, a weight sensor 57 fitted to the reservoir 56 stops the flow of sand, using the needle valve 51 and air tube 53, when the reservoir 56 is full. Any one or more of the bulk container 49, the binder container 36 and the mixing chamber 115 may also exemplify a reservoir of support material.

As stated earlier, the cementitious material may be agitated to maintain freshness. Figure 7 depicts the details of a stirrer arrangement 120 that allows continuous or periodic agitation of the cementitious material. The stirrer arrangement 120 may be disposed at any suitable location in the cementitious material delivery path, e.g. at the hopper 102 and worm pump 2 assembly shown in figure 1 or downstream thereof. The cementitious material is delivered to container 59 which includes a mixing or stirring paddle 62 and a vibrator 65. The mixing or stirring paddle 62 is rotatable by motor 60 by way of a shaft 61. Agitation of the material in the container 59 is performed by the motor 60 driving the shaft 61 and mixing paddle 62, and by the vibrator 65 shaking the container 59. The paddle 62 has a specific surface area, thus it requires a certain force to move it. The force, which indicates the stiffness of the material, can be measured by a torque measuring unit 63. A force measurement processor 64 monitors the torque required to rotate the paddle 62 and adjusts process parameters and frequency and amplitude of the vibrator 65 to assist the flow of cementitious material.

Thus, in a general aspect, the stirring paddle 62 and / or the vibrator 65 exemplify agitation means suitable for agitating cementitious material or stabilised cementitious material.

Figure 8 shows a vibrating nozzle arrangement 121 configured to compact material as it is being deposited and improve inter-layer bonding for wet materials as well as improving surface finish. The vibrating nozzle arrangement 121 can be deployed either for depositing build (cementitious) material or support material, i.e. it can be incorporated into the nozzle 13 or the nozzle 12 of figures 2 and 3a.

The exemplification of figure 8 shows the vibrating nozzle arrangement 121 serving as a cementitious material nozzle. Cementitious material may be delivered through the hose 18 or other conduit, e.g. via the roller pump 24. The hose 18 is retained in a nozzle head 122 and is vibrated vertically (as orientated in the diagram) by the vibrator 123, i.e. the vibration occurs in the direction parallel to the hose long axis and in the direction of extrusion. The vibrator 23 may be a piezo-electric stack connected to a power supply through wires 67. A voice coil or mechanical movement could also or alternatively be employed for larger amplitudes while the vibrator 123 remains fixed. The application of ultrasonic vibration to the deposition head nozzle could also or alternatively be used for smaller amplitudes for precise material control. Thus, in a general aspect, figure 8 provides a vibratable nozzle. The vibratable nozzle could be configured to vibrate the nozzle in a direction parallel to the nozzle axis. The nozzle axis, in this context, corresponds to the longitudinal axis of the hose and the direction of extrusion. A vibrating nozzle may improve the flow of material being extruded through the nozzle and or compact the extruded materials. The vibratable nozzle could be configured to vibrate the nozzle in a direction orthogonal to the nozzle axis. This may result in a different quality of surface without surface compaction.

Figures 9a and 9b show a variable diameter nozzle 130 configured to provide variable bead dimensions and variable bead aspect ratio. This allows higher density of fill for certain geometries and provides fast dynamic system response.

The variable diameter nozzle 130 can be deployed either for depositing build (cementitious) material or support material, i.e. it can be incorporated into the nozzle 13 or the nozzle 12 of figures 2 and 3a.

The exemplification of figures 9a and 9b shows the variable diameter nozzle 130 serving as a cementitious material nozzle 13. Cementitious material may be delivered through the hose 8 or other conduit, e.g. via the roller pump 24. The hose 18 is coupled into a hose housing 132 in nozzle 130 and the hose has multiple axial slots 131 cut to maximise closing movement. As shown in figures 9a and 9b, the axial slots 131 are preferably also slightly oblique to the long axis of the hose and preferably also somewhat oblique to the radial direction of the hose.

A motor and gearbox 68 are coupled to rotate a pinion gear 69, which engages and turns a ring gear 70 that is attached to a closing block 71. A thread 73 couples the ring gear 70 and closing block 71. Complementary tapered profiles 75 on each of the ring closing block 71 and hose housing 132 causes compression of the distal end 72 of the hose housing 132 when the closing block and nozzle 13 are axially displaced relative to one another using the thread 73. This causes the end of the hose housing 132 and hose 18 to reduce or increase in radius, thereby defining a variable diameter nozzle 130.

Other arrangements of variable diameter nozzle may be envisaged which allow changing of shape / cross-sectional profile of the nozzle. Thus, the expression "variable diameter" nozzle is intended to encompass a nozzle in which at least one cross- sectional dimension of a nozzle end can be varied. The cross-sectional profile need not be circular or elliptical, but could be rectangular, or other multi-sided shape. The hose need not have slots in it but could rely on pliancy, plasticity or elasticity of the hose material to contract or expand. A variable diameter nozzle whose orifice can be automatically adjusted in shape and / or size to change the cross-sectional profile of extruded material in a controlled and continuous manner can be particularly useful when a layer of material to be deposited requires the formation of one or more beads which are required to be smaller or narrower than the standard bead size for a printed layer of material. This may avoid the need to leave partial gaps or change nozzles when different resolutions of printed bead are required.

The main controller 110 may be used to control any function of the delivery apparatus 100 based on information / feedback received from the optical sensor 32, such as flow rate of material to the nozzles 12, 13, 35, 45 and extrusion rate therefrom. The optical sensor or sensors could be replaced by or supplemented with other types of sensor suitable for monitoring the texture, shape or form of the layers being printed by the apparatus 100. For example, sensors using other parts of the electromagnetic spectrum or ultrasound could be used.

Although the means for indexing the nozzles along a predetermined path has been generally exemplified by a robotic arm having pivoting sections, it is possible for this function to be performed by any suitable robotic arm assembly or structure capable of manipulating the nozzles 12, 13, 35, 45 to the required position in space and the required angular presentation. For example, a gantry system could be used which presents an x-y-z stage for the print head 101. The gantry system may comprise four columns with two supporting beams that track vertically. The two supporting beams in turn support a third beam that tracks along one horizontal axis that supports the print head. The print head can then track in the other horizontal direction along the third beam. Other arrangements are, of course, possible.

The main controller 110 is preferably a computer control means although application specific circuits could be deployed instead or in addition. The main controller can be a single central unit or could be distributed among the various component parts of the apparatus 100.

Although the cementitious deposition head nozzle 13 and the support material deposition head nozzle 12 of the preferred embodiments have been shown as having different angular presentations on the print head 101 (figure 2) so that they can each be rotated into position (figures 2a and 2b) for deposition on a surface 104, it will be understood that the cementitious material nozzle 13 and the support material nozzle 12 could alternatively be provided in the same orientation, and could be immediately adjacent one another, so as to provide for simultaneous deposition or more rapid switching between deposition of cementitious material and support material, for example.

Advantages of enabling the delivery of both cementitious material and support material in a "printing" type process is that a reduced, or minimum, volume and mass of cementitious material can be delivered to the point of use, reducing the cost and time for building and post-processing, clear-up and recycling time. The delivery paths for both cementitious material and the support material can be separately optmised for delivery to and from the same print head. This enables formation of structures that include hollow panels and components and doubly curved structures. The deposition process can be combined with other surface preparation or surface treatment techniques, e.g. for forming smooth surfaces, such as tamping, or by a vibration / oscillatory instrument, air jets or combinations thereof.

Other embodiments are intentionally within the scope of the accompanying claims.